Method of and apparatus for forming halftone dots

Details Method of and apparatus for forming halftone dots Method of and apparatus for forming halftone dots

1989-12-05

1992-05-12

Shoop, Jr., William M.

Facsimile and static presentation processing

Facsimile

Recording apparatus

358457, H04M 140

Patent

active

051132648

ABSTRACT:
Halftone dots are formed on the basis of three sets of screen pattern data assigned to the to a same combined area, in which a plurality of halftone dots are to be formed. The three sets of screen pattern data have different threshold values assigned to respective pixels in the combined area, and are stored in SPM's (101-116). Eight SPM's (Screen Pattern memory units) store a first set of the screen pattern data, six SPM's store a second one, end two SPM's store a third one. One of the sixteen SPM's is randomly selected with respect to each pixel, whereby one of the threshold values (D.sub.s) stored in the selected SPM is compared with an iamge signal (V.sub.1). A dot signal indicating whether or not each pixel is solid is produced on the basis of the comparison. Accordingly, a grid-like pattern of halftone dots to be seen in a highlight area or a shadow area is prevented.

REFERENCES:
patent: 4032978 (1977-06-01), Wong
patent: 4033443 (1977-07-01), Bunge et al.
patent: 4340912 (1982-07-01), Troxel
patent: 4578714 (1986-03-01), Sugiura et al.
patent: 4700235 (1987-10-01), Gall
patent: 4930023 (1990-05-01), Yakame

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